Condensation processes



United States Patent CONDENSATION PROCESSES Harold H. Zeiss and Walter Herwig, bay-ant, Ohio, s

signors to Monsanto Chemical'Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed June 2, 195a, Ser. No. 738,953 i 13 Claims. or. 260- 673) The present invention is directed to the polymerization of organic compounds containing unsaturated carbon-tocarbon or carbon-to-nitrogen bonds in the presence' of covalent chromium compounds, particularly tri-covalent organo chromium compounds. I

The invention is particularly directed to the condensation of Ir-electron systems to 6-membered'rings by'means 'of tri-covalent organo chromium compounds, and is'espe- In another aspect the invention is directed to the process of reacting together chromium halide, magnesium, an organic halide capable of forming a Grignard reagent, and an acetylene containing no acidic hydrogen to obtain arenes. a

The invention is further directed to trialkyl chromium compounds, the same being useful as condensation catalysts, particularly for the condensation of di-substituted acetylenes to substituted benzenes.

An object of this invention is to prepare catalysts suitable for the condensation of 1r-electron systems to 6-membered rings. A further object of the invention is to prepare covalent trialkyl chromium compounds in stable form. I

Another object of the invention is to provide a good method of synthesis of substituted benzenes from disubstituted acetylenes.

The tri-covalent chromium compounds utilized herein can be obtained by reaction of Grignard reagents with trivalent chromium compounds, and the organic portion of the chromium compounds can be any-organic radicals capable of forming Grignard reagents. Specific procedures suitable for the preparation of triaryl chromium compounds are described in our copending application, S.N. 698,376, filed November 25, 1957, and any of the procedures described therein, either generically or 'specifically, are also applicable here. The trialkyl chromium compounds can be prepared by corresponding procedures utilizing alkyl Grignard reagents as described herein below. It will be realized that effective catalysts can be produced in which the alkyl and aryl radicals aremodified by groups which do not prevent the production of Grignard reagents, this being particularly true in the case of inert substitutents which do not change the fundamental hydrocarbon character of the radicals. Any aroarom-atic structure, some tricyclic product is obtained, etc.

fa lC as the groups attached to chromium, the saturated hydrocarbon radicals ,being preferred in the case of non-cyclic radicals. In the'case of aryl radicals, mono-, di-, trior polycyclic radicals are suitable, e.g., benzenes, naphthalenes,"phenanthrenes, anthracenes, etc.; any of the aryl radicals disclosed in our aforesaid copending application S.N. 698,376 are also applicable here. As to the alkyl radicals attached to chromium, those straight or forkedchain alkyl radicals containing about 1 to 20 carbon atoms 'will ordinarily be employed, particularly those in the range of 1 to 10 or so carbon atoms; for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, n-pentyl and each of its isomers, n-hexyl, nheptyl, n -octyl, 2-ethylhexyl, nonyl, decyl, dodecyl, tridecyl (from 0x0. process), octadecyl, eicosyl, etc. As cycloalkyl radicals, cyclopentyl, cyclohexyl, etc. can most conveniently be employed. It is also possible to utilize unsaturated cycloaliphatics, e.g., cyclopentadienyl. The 'straightchain aliphatics can also be unsaturated, vinyl. allylfetc. groups being suitable.

' The course of our preferred process is indicated by the following reaction in which R is an organic, preferably hydrocarbon radical, and R' is an organic, preferably hydrocarbon radical. Only when R is phenyl is any of the naphthalene compound obtained. Of course, when R represents a bicyclic In the above reaction the R on one acetylene carbon atom is quite often the same, but can be diflferent, from that on the other acetylene carbon atom.

The polymerization reactions of the present invention are generally conducted in the presence of tetrahydrofuran, but any other Grignard solvent capable of complexing the trivalent chromium compounds to assure a fairly stable form thereof for reaction would be suitable.

It is presumed that the reaction involves replacement of the three complexing tetrahydrofuran molecules in a, for example, trialkyl chromium tri-tetrahydrofuranate with three molecules of acetylene, to give an intermediate complexfrom which the substituted benzenes are then formed.

matic or aliphatic halogen compounds are suitableso H It will be realized that any hydrocarbon radicals, including cycloalkyl radicals are suitable :One especially notable aspect of our invention is the fact that it is possible to react the reagents utilized in preparing the tri-covalent chromium catalyst, including even the magnesium turnings, simultaneously in the same reaction vessel with the m-substituted acetylene compound,

and obtain the substituted benzene compounds as products a Grignard reagent, and CrCl as an example of a trivalent chromium compound (THF represents tetrahydrofurau).

in general known compounds or homologs of same having recognized value in the field of synthetic organic chemistry, and can be used as .high boiling solvents, hydraulic fluids, plasticizers, lubricant or gasoline additives, organic intermediates, and the like.

It will be recognized, of course, that some types of products will have greater value than other types. However, the only essential feature of the inventionin polymerization is the discovery of a catalyst system which effects condensation of unsaturated systems.

'The importance and value of our invention is apparent item the "fact that it provides a new synthesis of aromatic molecules. Acetylenes are, of course an old and well known class of chemicals and extensive work has-been carried out in an effort to find useful "condensations of acetylenes. The present discovery now provides a procedure for condensing acetylenes under mild, controlled conditions to obtain specific,'identifiable aromatic compounds.

For an acetylene to condense to an aromatic compound according to the present inventiomitis necessary that it be \di-substituted. Any alkynes other than 1- alkynes are suitable for such purpose, for example, nonalpha alkynes of 4 to 2 0 or more carbon atoms, particularly the non-alpha alkynes of 4 to 10* carbon atoms. Suitable alkynes are, for example, those di-substituted tacetylenes in which the substituents are any of the straight or forked chain alkyl radicals named hereinabove with respect to suitable alkyl radicals attached to the chromium in the tri-covalent chromium compound, and, in fact, aryl and cycloalkyl substituents are also suitable and any of the aryl or cycloalkyl radicals named with respect to the chromium above are also suitable substituents for the acetylenes to be condensed to substituted benzenes. Moreover, acetylenes substituted by heterocyclic substituents are also suitable and produce benzenes containing heterocyclic substi-tuents. As specific examples of non-alpha alkynes and other di-subst-ituted acetylenes suitable for conversion to substituted benzenes, the following can be mentioned: Z-butyne, 2-

*pentyne, 2-hexyne, 3-hexyne, 2-octyne, 3-octyne, 2,2-

dimethyl-3-hexyne, 2-methyl-3-heptyne, S-decyne, 4-dodecyne, 6-hexadecyne, Z-eicosyne, dicarbethoxyacetylene, diphenylacety-lene, a-phenyl-Bmethylacetylene, tat-phenylmethyl-fi-methylacetylene, dim-naphthylacetylene, l-anthracyl-propyne, p-tolylethylpropyne di-p-tolylaacetylene, u-xylyl-B-methylacetylene, etc.

It is also possible to utilize mono=substituted acetylenes,

or acetylene itself, but in such cases the reaction goes predominantly to the production of polymeric materials rather than to the lower cyclic condensates. Nevertheless, the condensation reactions of these molecules such as, for example, phenylacetylene, methylacetylene, ethylacetylene, fi-naphthylacetylene, cyclohexylacetylene, etc., or carboxyethylacetylene, hydroxyethylacetylene, etc, over tri-eovalent chromium produce usefiul products and are considered part of the present invention.

-In addition to the ring-forming :condensations which are extensively described herein by way of'example, it will now be realized that unsaturated compounds such as olefins,-e.g., 21butene, will condense with trieeovalent chromium to form saturated ring systems, for example, cyclohexanes such as hexarnethylcyclohexane; or nitriles, e.g., methyl cyanide, can be condensed to dorm triazines, e.g., triInethyl-1,3,5-triazine.

,In general .the reactions described herein, .as exemplified by the heterogeneous. reaction of triphenylehromium .tri-tetrahydrofuranate with 'Z-butyne, .take place fairly rapidly circa room temperature -and are followed by hydrolysis and ether extraction .to obtain a mixed crystalline product which can be separated by fractional crystallization ofsuch derivatives as the .picrates.

ZI'he followingexamples are illustrative of certain embodiments of the invention. .Inlthe eXam Ies Z-butyne is employed .as exemplary of di-substituted acetylenes, and ,pheny-lacetylene is exemplary of mono-substituted :acetylenes.

EXAMPLE 1 W800 :rnl. .t-etrahydrofuran solution of triphenyl :chromi-um containing 67.2 ,millimoles of the triphenyl chromium was placed in arfiask under nitrogen and ml. (5135 moles) .of Z-butyne (B.P. 27, dried over :Drierite.) waszadded atj'room 'temperature. In about 15 minutes reaction occurred and the temperature rose to 50 .C.,.and'the mixture .rbecame brown-black in color. About two-thirds of the solvent was removed by distillation under vacuumwat.3.0 C.,;and.the.residue was hydrolyzed by addition of 30.6 liter of water. The'resultsing .hYdIOlYSiS mixture was filtered to remove a dark salt and give a yelloworangefiltrate. ,An aqueous solution of sodium tetraphenylboron was added to :the filtrate and :15 grams of .tetraphenylboron,saltprecfitated. The salt exhibited,goodstabilityin organic solvents but decomposed.topsomelextent.upontstanding about one hour in acetone. 'Iihe acetone was evaporated and the residue iwasnhen sublimed to givegcolo'rless crystals of hexamethyl benzene, M.P. 15.8460 ,C;;.;a mixed melting point with pure hexamethyl benzene was 16*1,.1.64 :C. Infrared vanalysis indicated vthecompound towbe hexamethyl benzeneadmixed with less than ,5%, .1,2,3,4-.tetramethylnaphthalene. A sample of the tetraphenylboron salt of pure bishexamethy-lbenzene chromium prepared by an entirely different procedure showed the samestability in solvents'as the above tetraphenylboron salt, and its decomposition in acetone .gave pure hexamethylbenzene.

salt filtered from the hydrolysis mixture above was treatedwith 2 N sulfuricaci'd and-the resul-tingrnixture was extracted three times with .ether. The ether extracts were concentrated and .1093 grams .of solids crystallized. .A 'hOL'CQHCfiHlLDflIBd solution of the solids in ethanol wassrnixed withacold,.saturated ethanol so- .lution containing 11.6 .grams of picric acid, to :produce 1-2-3 .4 .grams of an orange ipicrate. Stepwise concentration :of .:a .warm solution-of this picrate gave 6 or '7 crystal -finactions, :of which the first two were orange-red needles -of pure 1,-2,3,4 tetramethylnaphthalene picrate, 'M.P.

Antilysis.-Calcd. for C dH Ngot. C, 58.11; H, 4.63; "N, 10.17. "Found: C, 5.8;l3;,H, 4.34; N, 10.55.

"Cleavage of the picratewith aqueous ammonia yielded purel;2;3,4-tetramethylnaphthalene, ML-P. -10 7-108.5 C. Analysis-Calm. ffor .C H C, 91.25; H, 8.75.

Found. 0, 91.45; H, 8.59. The analysis was confirmed by infrared and ultraviolet analyses.

The end fraction of the above finactional crystallization consisted mainly of hexamethylbenzene picrate, which was purified by recrystallization to pure hexamethylbenzene, M.P. 175-176 C. Cleavage with aqueous ammonia gave hexamethylbenzene, M.P. 165-167 C. A mixed melting point with a known sample of hexamethylbenezene was 165- 167 C. -Oareful fractional recrystallization of the intermediatefractions from the above fractional crystallization gave total amounts of 4.70 1,2,3,4-tetramethylnaphthaleneand 5.32 grams of hexamethylbenzene, for yields respectively of 38.0% and 48.8% (based on triphenylchromium).

EXAMPLE 2.

A condensationwas carried outaecording to the procedure of Example 1 except that a triphenylchromium to Z-butyne rnol ratio of 1:3 was employed in place of the 1:20 mol ratio of Example 1, only 15.7 of 2- hutyne being employed. -Inabout 90 minutes exo thermic reaction and color change was apparent. After standing for about three days, the solution was concentrated, hydrolyzed and filtered to give a solid salt and an orange filtrate. An aqueous sodium tetraphenylboron solution was .added and the resulting precipitate was dis- 'solved in acetone and filtered from chromium hydroxide flakes which developed to give a practically colorless solution. The acetone was replaced by ethanol, and addition of picric acid caused precipitation of 0.28 gram 1,2,3,4 tetramethylnaphthalene picrate, M.P. 182-184 C. Cleavage with aqueous ammonia gave pure 1,2,3,4- tetr-amethylnaphthalene. The salt from the filtration above was treated as in Example 1 to give 4.7 grams of 1,2,3,4-tetramethylnaphthalene by crystallization as the picrate from ethanolic solution. A second fraction from the ethanol yielded additional compound. The total of 5 grams 1,2,3,4-tetramethylnaphthalene represents a yield of 40.3% (based on triphenylchr-ornium). The colorless ethanolic mother liquor upon dilution with aque 'ous ammonia yielded a 1.4 gram precipitate of diphenyl, M.P. 69.570 C. It will be noted that in this example 1,2,3,4etetnamethylnaphthalene was obtained in yield substantially equivalent to that of Example 1, but no hexamethylbenzene was produced. The effect of the mol ratio of triphenylchromium to butyne in controlling the relative amounts of the condensation products is further shown in Table I.

Table I Time to Start Yield of Yield of (C HmGnButyne Me] of Reaction, Hexamethyl- Tetramethyl- Ratio min. benzene, naphthalene,

Percent Percent three hours, hydrolyzed and extracted with ether, but

evaporation of the extracts left no residue.

('B) A50 ml. solution of tetrahydrofuran saturated with chromium tric'hloride was treated with 2 ml. butyne and then treated as in (A), but no residue was obtained.

' '(C) A 1 gram amount of powdered chromium trichloride tritetrahydrofuranate wastreated with 9 ml. butyne,

6 but no condensation product was obtained even after standing for four days.

EXAMPLE 3 5 An ethyl magnesium bromide solution was prepared from 9.8 grams ethylbromide, 3 grams magnesium and 300 ml. tetrahydrofuran. The yield by titration was 89% (80 millimoles). The solution was added dropwise withstirring to a 100 ml. tetrahydrofuran solution 'IcontaininglOJ grams chromium trichloride tri-tetrahydrofuranate (27 millimoles) at C. Reaction started immediately and was complete in one hour to produce triethylchromium tetnahydrofuranate. A 45 ml. amount of Z-butyne (31.2 grams, 0.58 mole) was then added at --20 C. and the resulting mixture was kept at room temperature for three days. The black-brown solution was heated under vacuum at 30 C. to remove solvent, and the brown residue was then mixed with ethyl ether and 2 N sulfuric acid. The resulting green ether layer was concentrated, diluted with ethanol, and cooled to 0 C. to yield 2.40 grams of colorless crystals, M.P. l5516l C. Distillation of the mother liquor under highvacuum gave 0.25 gram crystals, M.P. 152-160" C., for a total yield of fairly pure hexamethylbenzene of 2.65 grams, or 60.3% (based on triethylchromium). Recrystallization was practically quantitative and gave hexamethylbenzene of melting point, 163l64 C. The absence of a tetramethylnaphthalene from the product when triethylchromium is employed as catalyst further confirms the formation of intermediates from the organo chromium compound in the reaction.

EXAMPLE 4 An a-naphthyl magnesium bromide solution was prepared from 10.35 grams tat-naphthalene bromide, 2.4 grams magnesium and 95 ml. tetrahydrofuran. The solution had a concentration of about 45 millimoles ot-naphthyl magnesium bromide in 100 ml. solution. At C. 66 ml. of the Grignard solution was added with stirring to 60 ml. tetrahydrofuran to which 3.72 grams chromium trichloride tri-tetrahydrofurauate had been added. The reaction started immediately and the mixture became wine-red in color. To the solution of tri(otnaphthyl)chromium, 2.34 ml. of Z-butyne was added with stirring at room temperature; the exothermic reaction was controlled by ice water-cooling. The reaction mixture was hydrolyzed with ice water and extracted with ether. The extracts were concentrated and diluted with alcohol and then boiled to remove ether. At 0 C., 1.01 grams of crystalline material was obtained. Sublimation of this material at 80 C. under vacuum gave 0.68 gram naphthalene as sublimate, and 0.33 gram 1,2,3, 4-tetramethylphenanthrene as residue; the phenanthrene compound had a melting point of 85-86 C., and the picrate derivative melted at l39-l41 C. The ethanol mother liquor above was treated with an ethanol solution of picric acid, and aditional product was obtained in the form of thepicrate. The total yield of 1,2,3,4-tetramethylphenanthrene was 1.02 grams. The compound was recrystallized from ethanol to give colorless flakes, M.P. 87-89 C.

AnaZysis. -Calcd.: C, 92.26; H, 7.74. Found: C, 92.27; H, 7.90. This compound is of interest as a high energy fuel and also has utility as an organic intermediate, in preparing, for example, the corresponding diphenic acid by recognized procedures. Other l,2,3,4-tetraalkylphe- 'nanthrenes have similar value, particularly those in which the alkyl radical is a straight or forked chain radical of 1 to 4 carbon atoms.

70 EXAMPLE 5 To a solution of 16.7 millimoles triethyl chromium in 120 ml. tetrahydrofuran prepared according to the procedure of Example 3 was added 8.5 grams of phenylacetylene. The mixture became brown-black in colorin about one hour, and after standing for two days'was hydrolyzed, acidified with 2 N sulfuric acid and extracted with ether. The solvent was evaporated from the .extracts to leave a dark-oil which -was treated with ethanol to give a brown amorphous powder of softening point '6-5-88 C. The polymeric material had properties making it-useful as an absorbent or a filler material for synthetic resins.

EXAMPLE 6 hydrolysis. Boiling the mixture before hydrolysis resulted in a brown amorphous powder.

EXAMPLE 8 At room temperature 0.5 gram chromium trichloride tritetrahydrofuranate, 1 gram powdered magnesium, 3 ml. 2-butyne and 15 ml. bromobenzene were mixed and stirred in a Schlenk tube. After 10 minutes a slight temperature rise was observed as the color of the mixture changed slowly from violet to red brown. After several hours the mixture became brown-black in color. The mixture was permitted to stand two days and was then hydrolyzed and extracted with ether. The ether extracts were concentrated to a'small volume by evaporation of the ether, and some unchanged bromobenzene under vacuum. The residue was dissolved in glacial acetic acid and a salt was precipitated from the-solution. The salt was recrystallized from ethanol to yield 0.12 gram'of product which infrared analysis indicated to be 80% hexamethylbenzene and 20% 1,2,3,4-tetramethy1- naphthalene. The total yield of substituted benzenes was 54% (based on chromium). Thus, it is possible to utilize a heterogeneous reaction procedure in which 2- butyne is present in the reaction mixture with reactants capable of producing the triphenyl chromium compound, and in which the various reactions occur simultaneously, and it is not necessary to employ a step-wise procedure to produce the various intermediates. The heterogeneous reaction procedure is generally applicable to the condensation of the di-substituted acetylenes with the tricovalent chromium compounds as disclosed herein, and is applicable to the representative examples of the reactants as disclosed herein. However, in order to effect the reaction in one step as described above, it is necessary to employ the chromium halide in the form of its tetrahydrofuranate.

The present, invention, of course, involves a novel reaction rather than specific conditions for carrying out such reaction. However, the following conditions will ordinarily be observed. The mol ratio of organo chromium to acetylenic compound will generally be in the range of about 1:1 to 1:20, but it is generally necessary to have at least 3 moles of acetylenic compound present if the maximum utilization of organo chromium compound in the preparation of substituted naphthalenes is to be effected. Of course, naphthalenes will be produced only when the chromium in the organo chromium compound contains phenyl substitutents; when 5 to 20 or more moles of acetylenic compound are present for each mole of organo chromium, the substituted naphthalenes are accompanied by monocyclic substituted benzenes, but the yield of naphthalenes is not diminished. When an alkyl chromium reactant is employed, mol ratios of chrocompound to acetylenic compound from 1:1 to

1:20, or greater or lesser, can be employed, and the yield based on chromium rcompound will generally .improve 8 with increasein the relative amounts of ace'tylenic com pound.

The condensation reactions can be considered attemperatures varying from about -50C. to -+70, C -or to about the boilingpointof tetrahydrofuran or the like, depending to some extent on the reactivity of the re: actants, and can conveniently be effected by mixing the catalyst at lower temperatures and completing the reaction at higher temperatures; temperatures of the order of 10 to 30 C. or soor approximately room temperatures can conveniently be employed. The reactions can take .from a few minutes-to several hours, but in order to insure complete reaction and maximum yields the reaction mixture can be permitted to stand several days. The reaction is conducted underusual Grignard conditions as understood by-those skilled in the art with exclusion of oxygen, moisture, etc.

The organo chromium compounds herein are referred to as catalysts as the end-result of the reactions is the condensation of unsaturated molecules with each other, but use of the term catalyst is not meant to imply that the organo chromium compound is not destroyed in the reaction. However, the success of the oneistep reaction in Example 8 above presents the possibility of regenerating the catalyst in situ by addition of reactants during the condensation process.

As the chromium halide for use in our invention, anhydrous chromicchloride is very suitable, and chromic bromide and chromic iodide are also effective. Ohromyl chloride (CrO Cl is also suitable.

What we claim is:

'1. The process of preparing benzenes and naphthalenes which comprises reacting acetylenes containing no acidic hydrogen with triarylchromium compounds to produce said benzenes and naphthalenes.

2. The process of preparing benzenes and naphthalenes which comprises treating non-alpha alkynes in tetrahydrofuran solution with triarylchromium, the mol ratios of triaryl chromium to alkyne being in the range oflzlto 1:20.

3. The process of claim 2 in which triphenyl chromium is employed.

4. The process of preparing tetramethylnaphthalene which comprises mixing dimethylacetylene and triphenylchromium in tetrahydrofuran in mol ratio of chromium compound to acetylene of from 1:1 to 1:20.

5. The process of claim 4 in which hexamethylbenzene is also produced.

6. The process of preparing monocyclic aryl hydrocarbons which comprises reacting acetylenes containing no acidic hydrogen with trialkylchromium compounds to produce monocyclic aryl hydrocarbons.

7. The process of preparing benzenes which comprises reacting an alkyl Grignard reagent with chromic trichloride and then treating with an acetylene'conta-ining no acidic hydrogen.

8. The process of preparing hexaaJkyl benzenes which comprises treating ethyl magnesium bromide with chromic trichloride in tetrahydrofuran and'then with a dialkylacetylene.

9. The process of preparing hexamethyl benzene which comprises treating ethyl magnesium bromide with chromic trichloride in tetrahydrofuran and then treating with dimethylacetylene.

10. The process of preparing aromatic compounds selected from the group consisting of benzenes, naphthalenes and phenanthrenes which comprises reacting together chromic halide tetrahydrofuranate, magnesium, organohalogen compound capable of forming an organornagnesium halide Grignard reagent with magnesium, and a non-alpha alkyne to produce said aromatic compounds selected from the group consisting of benzenes, naphthalenes and phenanthrenes.

11. The process of claim 10 in which an organomag- .nesiumhalide Grignard reagent is .formsdfrorn the maghesium and organohalogen compound, which is then re- FOREIGN PATENT acted with the chromium halide tetrahydrofuranate followed by g withthe non alpha 533,362 13613111111 y 16, 1955 -12. The tprofiess of gngatzrilngG henagthlreenes 6 OTHER REFERENCES comprises rea ng a n p i y ngn'ar agen W1 chromic tI'iChilOFide and then treating with an acetylene Angewandte Chemle, Volume 68, page 438, July 7, containing no acidic hydrogen. 1956' 13, T i lk l h m mq h d f m Berger et 'aL: Chem. Abs-tracts, vol. 37, page 1764,

see. 8, Apr. 10, 1943. References Cited in the file of this patent 10 UNITED STATES PATENTS 2,324,073 G aylor et a1 July '13, 1943 2,772,314 Campbell Nov. 27, 1956 

1. THE PROCESS OF PREPARING BENZENES AND NAPHTHALENES WHICH COMPRISES REACTING ACETYLENES CONTAINING NO ACIDIC HYDROGEN WITH TRIARYLCHROMIUM COMPOUNDS TO PRODUCE SAID BENZENES AND NAPHTHALENES. 